Age at which participants could elect to remain in the defined benefit plan as of August 31, 2008.

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- Definition

Independent Insurance Agencies and Brokerages

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- Definition

Number of Locations

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- Definition

Number of Subsidiaries

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- Definition

Percentage of earned premiums.

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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-Publisher FASB

-Name Accounting Standards Codification

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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The number of states the entity operates in as of the balance sheet date.

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- Definition

Other investments not otherwise specified in the taxonomy.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Fair value amount of the specified investment category of assets maintained in separate accounts as of the balance sheet date.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term of exercisable stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 reporting_locations subsidiary state independent_insurance_agency	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2008
Significant Accounting Policies
Number of operating subsidaries	2cinf_NumberOfSubsidiaries
Number of independent insurance agencies	1,466
Number of reporting locations	1,884cinf_NumberOfLocations
Number of states in which entity operates	39
Defined Benefit Plan Qualifying Age				40 years
Current fair value of the BOLI invested assets and cash exceeded the current fair value of the contract holders' account value	$ 47
Other invested assets	68us-gaap_OtherInvestments	68us-gaap_OtherInvestments
Depreciation expense	37us-gaap_Depreciation	37us-gaap_Depreciation	37us-gaap_Depreciation
Land, building and equipment impairments	0us-gaap_AssetImpairmentCharges	0us-gaap_AssetImpairmentCharges	0us-gaap_AssetImpairmentCharges
Minimum
Significant Accounting Policies
Estimated useful lives	3 years
Maximum
Significant Accounting Policies
Estimated useful lives	39 years 6 months
Life Policy Loans
Significant Accounting Policies
Other invested assets	31
Venture Capital Funds
Significant Accounting Policies
Other invested assets	$ 37
10 Largest States
Significant Accounting Policies
Generated percentage of total earned premiums	62.80%	63.80%
Ohio, Largest State
Significant Accounting Policies
Generated percentage of total earned premiums	17.70%	18.50%
Indiana, Illinois, Pennsylvania, Georgia, Michigan and North Carolina \| Minimum
Significant Accounting Policies
Generated percentage of total earned premiums	5.00%
Indiana, Illinois, Pennsylvania, Georgia, Michigan and North Carolina \| Maximum
Significant Accounting Policies
Generated percentage of total earned premiums	8.00%
Largest Single Agency Relationship
Significant Accounting Policies
Generated percentage of total earned premiums	0.80%
All Other \| Maximum
Significant Accounting Policies
Generated percentage of total earned premiums	2.10%
Stock Options
Significant Accounting Policies
Awards vesting period	3 years
Weighted-average remaining contractual life for options expected to vest	10 years
Restricted Stock Units
Significant Accounting Policies
Awards vesting period	3 years
Property Casualty Insurance Segment
Significant Accounting Policies
Number of operating subsidaries	2